Methods of this kind are known from the state of the art in great variation and are primarily utilized in measuring apparatus for gearing. With these measuring apparatus, the involute profiles of the tooth flanks of the gear wheels can be measured.
U.S. Pat. No. 4,852,402, for example, discloses such a method for measuring the involute teeth of a gear wheel. For this purpose, the gear wheel to be measured is arranged on a rotational unit which rotates the gear wheel to be measured. Furthermore, a probe, which measures in a measuring axis, is passed by the teeth flanks of the gear wheel in such a manner that the probe moves over the tooth flanks of the rotating gear wheel and always scans the tooth flanks in one and the same preferred measuring direction. In order to always maintain the preferred measuring direction, the probe is guided by the mimic on a tangent to the base circle of the gear wheel. Here, the mathematical definition of the involute is utilized, namely, that the involute is always perpendicular to a tangent to the base circle of the gear wheel.
A gearing measurement apparatus, with which a similar method can be carried out, is disclosed in European patent publication 0,131,537. The gearing measurement apparatus disclosed in this publication differs from that shown in U.S. Pat. No. 4,852,402, inter alia, in that the probe additionally has a rotational axis about which the probe is rotated when scanning the tooth flanks. The probe is here guided in such a manner that the measurement axis of the probe and therefore the preferred measurement direction of the probe is always guided normally to the involute profile. To control the rotation unit of the workpiece as well as the rotation unit of the probe and the mimic of the probe, the mathematical characteristic of the involute is here likewise utilized so that the involute is, at each point, perpendicular to a tangent to a base circle of the gear wheel.
Swiss Patent 617,264 discloses a movably guided probe having a measuring axis. With the probe, the surface of the workpiece to be measured can be scanned. The probe has a mechanical arrangement via which the measuring axis of the profile measuring probe can be adjusted. To measure a workpiece, the probe is guided by a numeric control in such a manner that the probe is moved on a pregiven path along the workpiece. At the same time, the measuring axis is adjusted in such a manner that the probe exhibits, in each case, a defined preferred measuring direction on the surface of the workpiece. There is no suggestion in this patent as to the generation of the control data.
What is special with respect to the methods and arrangements described is that, when scanning workpieces, a fixed preferred measuring direction with which the probe scans the workpiece can only be realized via complex mathematical individual solutions. This applies also to the solution shown in Swiss Patent 617,264 even though it remains completely unanswered as to how precisely the control data for the corresponding coordinate measuring apparatus are generated. It must be here assumed that either mathematical individual solutions are used in a manner similar to that disclosed in European patent publication 0,131,537 or in U.S. Pat. No. 4,852,402 or the control data arise on the "drafting board".
At this point, it is appropriate to provide a definition of the term "preferred measuring direction". A preferred measuring direction is understood in the following to be that direction in which the probe is deflected out of its desired contour, preferably when there are deviations of the workpiece. For single-axis probes, this direction is fixed by the measurement axis in which the probe can only be deflected. For multi-axes probes wherein the probe pin can be deflected in at least two mutually perpendicular directions, the preferred measurement direction is defined by the measuring force with which the probe pin is pressed upon the surface of the workpiece. In case of optical probes having a scanning beam, the preferred measurement direction corresponds to the direction of the scanning beam.